One image forming apparatus known in the art is an electrophotographic color printer having a conveying belt disposed in confrontation with four photosensitive members corresponding to the four colors black, yellow, magenta, and cyan. However, the photosensitive members in this image-forming device are constantly in contact with the conveying belt. Therefore, even during operations to form images using only black, for example, the photosensitive members corresponding to the remaining colors yellow, magenta, and cyan remain in contact with the conveying belt and, consequently, wear more quickly.
Therefore, color image recorders have been proposed as image-forming devices capable of preventing such unnecessary wear and deterioration of the photosensitive members. For example, a color image recorder configures yellow, magenta, and cyan image-forming parts as a single color image-forming unit, and a black image-forming part as a single image-forming unit. With this image recorder, the color image-forming unit is separated from the conveying belt when forming black images.
However, in the color image recorder described above, the black image-forming part and color image-forming unit are operated independently. This configuration can potentially lead to fluctuations in the gap between the black image-forming part and the color image-forming unit during operations, making it difficult to maintain a uniform interval between neighboring photosensitive members. Maintaining this uniform interval between neighboring photosensitive members is extremely important for preventing color registration problems in color printers.